1. Field of the Invention
The present invention relates generally to semiconductor fabrication, and more particularly, to methods and apparatuses for using H2O vapor as a processing gas for stripping photoresist material from a substrate having a patterned photoresist layer previously used as an ion implantation mask.
2. Description of the Related Art
During semiconductor fabrication, integrated circuits are created on a semiconductor wafer (xe2x80x9cwaferxe2x80x9d) composed of a material such as silicon. To create the integrated circuits on the wafer, it is necessary to fabricate a large number (e.g., millions) of electronic devices such as resistors, diodes, capacitors, and transistors of various types. Fabrication of the electronic devices involves depositing, removing, and implanting materials at precise locations on the wafer. A process called photolithography is commonly used to facilitate deposition, removal, and implantation of materials at precise locations on the wafer.
In the photolithography process, a photoresist material is first deposited onto the wafer. The photoresist material is then exposed to light filtered by a reticle. The reticle is generally a glass plate that is patterned with exemplary feature geometries that block light from passing through the reticle. After passing through the reticle, the light contacts the surface of the photoresist material. The light changes the chemical composition of the exposed photoresist material. With a positive photoresist material, exposure to the light renders the exposed photoresist material insoluble in a developing solution. Conversely, with a negative photoresist material, exposure to the light renders the exposed photoresist material soluble in the developing solution. After the exposure to the light, the soluble portions of the photoresist material are removed, leaving a patterned photoresist layer.
The wafer is then processed to either deposit, remove, or implant materials in the wafer regions not covered by the patterned photoresist layer. After the wafer processing, the patterned photoresist layer is removed from the wafer in a process called photoresist stripping. It is important to completely remove the photoresist material during the photoresist stripping process because photoresist material remaining on the wafer surface may cause defects in the integrated circuits. Also, the photoresist stripping process should be performed carefully to avoid damaging the electronic devices present on the wafer.
As with many other wafer fabrication processes, an ion implantation process utilizes photolithography to protect specific areas of the wafer where ion implantation is not desirable. The ion implantation process, however, introduces difficulty in removing the photoresist material during the subsequent photoresist stripping process. Specifically, during the ion implantation process, ions penetrate into the outer regions of the photoresist material causing chemical bonds in the photoresist material outer regions to become cross-linked. Thus, the cross-linked outer regions of the photoresist material form a photoresist crust which is difficult to remove during the photoresist stripping process.
FIG. 1A is an illustration showing a cross-section of a patterned photoresist layer previously used as an ion implantation mask, in accordance with the prior art. During the ion implantation process, ions 131 are implanted into target regions 129 of a substrate material 121, where the target regions 129 are not protected by the photoresist material. Ions 131 entering the photoresist material cause the chemical bonds in the photoresist material to become cross-linked. Since the ions 131 only penetrate a limited distance through the photoresist material, the cross-linked photoresist is found near the outer portions of the photoresist material. The cross-linked photoresist is commonly called photoresist crust. The photoresist crust is typically characterized by a top photoresist crust 125 and a side photoresist crust 127. The thickness of the photoresist crust is generally dependent on the dosage of implant species and the ion implant energy in the photoresist material. Since the ions generally bombard the photoresist material in a downward direction, the top photoresist crust 125 is generally thicker than the side photoresist crust 127. The unaffected photoresist material underneath the photoresist crust is referred to as a bulk photoresist material 123.
Generally, the stripping process for photoresist materials used in wafer fabrication processes other than ion implantation involves heating the photoresist material to a sufficiently high temperature to cause the photoresist material to be removed through volatilization. This high temperature photoresist stripping process is commonly called ashing. Ashing, however, is not appropriate for stripping photoresist material that has been used as an ion implantation mask. Specifically, the photoresist crust is resistant to the ashing process. As the temperature increases, the pressure of the volatile bulk photoresist portion underneath the photoresist crust increases. Eventually, at high enough temperature, the bulk photoresist portion will xe2x80x9cpopxe2x80x9d through the photoresist crust. Such xe2x80x9cpoppingxe2x80x9d causes fragments of the photoresist crust to be spread over the wafer and the chamber. The photoresist crust fragments adhere tenaciously to the wafer. Thus, removal of the photoresist crust fragments from the wafer can be difficult if not impossible. Furthermore, the ion implantation process often uses elements such as arsenic which can present a serious hazard when contained in photoresist crust fragments being cleaned from the chamber. Therefore, removal of the photoresist crust is generally performed at a low enough temperature to prevent popping.
FIG. 1B is an illustration showing the problem wherein the bulk photoresist portion pops through the top photoresist crust, in accordance with the prior art. The bulk photoresist portion 123 is shown popping through the top photoresist crust 125 at a location 141. The resulting top photoresist fragments 143 are shown adhering to the substrate material 121.
Stripping of the photoresist crust at low temperature is typically performed by exposing the photoresist crust to radicals formed from various processing gases such as O2:N2H2, O2:N2:CF4, NH3, O2, O2:CF4, and O2:Cl2, where xe2x80x9c:xe2x80x9d denotes a gas mixture. The radicals serve to break the cross-linked chemical bonds of the photoresist crust, thus allowing the photoresist crust to be removed. Photoresist stripping using these processing gases at low temperature typically requires an extended amount of time, thus reducing wafer throughput. Also, handling some of these processing gases such as N2H2, NH3, and Cl2 generally involves special requirements and safety features which can increase the capital cost of the wafer processing equipment. Furthermore, photoresist stripping using these processing gases commonly results in a problem wherein the side photoresist crust is removed before the top photoresist crust, thus allowing the bulk photoresist portion to be removed from underneath the top photoresist crust. This problem is commonly called xe2x80x9cbulk photoresist undercutxe2x80x9d.
FIG. 1C is an illustration showing the undercut problem wherein the side photoresist crust is removed allowing the bulk photoresist to be undercut, in accordance with the prior art. The side photoresist crust (not shown) is removed prior to the top photoresist crust 127. Removal of the side photoresist crust causes the bulk photoresist portion 123 to be exposed to the radicals. Exposure of the bulk photoresist portion 123 to the radicals along with the volatile nature of the bulk photoresist portion 123 causes an undercut 151 region to be created. The undercut region 151 leaves the top photoresist crust 127 susceptible to breaking off or falling onto the substrate material 121. If allowed to contact the substrate material 121, the top photoresist crust 127 will adhere tenaciously causing its removal to be difficult if not impossible.
In view of the foregoing, there is a need for a method and an apparatus for stripping photoresist material that has been used as an ion implantation mask. Specifically, the method and apparatus should avoid the problems of the prior art by using a processing gas that can more efficiently and economically strip the photoresist material while preventing popping and undercut of the bulk photoresist.
Broadly speaking, the present invention fills these needs by providing an apparatus and method for using H2O vapor as a processing gas for stripping photoresist material from a substrate having a patterned photoresist layer previously used as an ion implantation mask. The patterned photoresist layer is characterized by a photoresist crust covering a bulk photoresist portion. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below.
In one embodiment, a method for stripping photoresist material from a substrate in a chamber is disclosed. The method includes providing a substrate having a patterned photoresist layer that has previously been used as an ion implantation mask. The previous use of the patterned photoresist layer in an ion implantation process formed a photoresist crust on an outer surface of the patterned photoresist layer. Thus, the patterned photoresist layer is defined by a bulk photoresist portion and the photoresist crust. In accordance with the method, the substrate is placed in the chamber and heated in the chamber. The method further includes providing H2O vapor to be transformed into a reactive form of H and a reactive form of O. The reactive forms of H and O react with the photoresist crust to remove the photoresist crust from the bulk photoresist portion of the patterned photoresist layer.
In another embodiment, a method for stripping photoresist material from a substrate in a chamber is disclosed. The substrate has a patterned photoresist layer that has been previously used as an ion implantation mask such that a photoresist crust is formed on an outer surface of the patterned photoresist layer. Thus, the patterned photoresist layer is defined by a bulk photoresist portion and the photoresist crust. The substrate is placed on a chuck in the chamber. The method includes providing H2O vapor to an applicator tube and applying microwave power to the H2O vapor in the applicator tube. The H2O vapor is transformed into H radicals and O radicals. The method further includes flowing the H radicals and the O radicals from the applicator tube to the substrate. Upon reaching the substrate, the H radicals and the O radicals react with the photoresist crust to remove the photoresist crust from the bulk photoresist portion of the patterned photoresist layer.
In another embodiment, a method for stripping photoresist material from a substrate in a chamber is disclosed. The substrate has a patterned photoresist layer that has been previously used as an ion implantation mask such that a photoresist crust is formed on an outer surface of the patterned photoresist layer. Thus, the patterned photoresist layer is defined by a bulk photoresist portion and the photoresist crust. The substrate is placed on a chuck in the chamber. The method includes providing H2O vapor to the chamber. In accordance with the method, radio frequency power is applied to the H2O vapor in the chamber to transform the H2O vapor into a plasma containing H ions, H radicals, O ions, and O radicals. The method further includes applying a bias voltage to the chuck to attract the H ions and the O ions to the substrate. Upon reaching the substrate, the H ions and the O ions react with the photoresist crust to remove the photoresist crust from the bulk photoresist portion of the patterned photoresist layer.
In another embodiment, an apparatus for removing a patterned photoresist layer from a semiconductor wafer is disclosed. The apparatus includes a chamber having an internal region configured to contain a plasma. A semiconductor wafer support structure is disposed within the chamber internal region. The semiconductor wafer support structure is configured to hold a semiconductor wafer in exposure to the plasma. An H2O vapor supply line is configured to supply an H2O vapor to a plasma generation region. The apparatus further includes a power supply for generating the plasma in the plasma generation region. The plasma generation region is configured to supply the plasma to the chamber internal region.
In another embodiment, an apparatus for removing a patterned photoresist layer from a semiconductor wafer is disclosed. The apparatus includes a chamber having an internal region defined by a top, a bottom, and sides. A semiconductor wafer support structure is disposed in close proximity to the bottom of the chamber internal region. The semiconductor wafer support structure is configured to hold a semiconductor wafer having a patterned photoresist layer. The apparatus also includes an applicator tube in open communication with the top of the chamber internal region. An H2O vapor supply line is configured to supply H2O vapor to the applicator tube. The apparatus further includes a power supply configured to apply microwave power to the applicator tube. The microwave power is used to transform the H2O vapor into H radicals and O radicals. The H radicals and the O radicals flow through the chamber internal region to reach the patterned photoresist layer of the semiconductor wafer. Upon reaching the patterned photoresist layer of the semiconductor wafer, the H radicals and the O radicals react to remove at least a portion of the patterned photoresist layer.
In another embodiment, an apparatus for removing a patterned photoresist layer from a semiconductor wafer is disclosed. The apparatus includes a chamber having an internal region defined by a top, a bottom, and sides. A semiconductor wafer support structure is disposed in close proximity to the bottom of the chamber internal region. The semiconductor wafer support structure is configured to hold a semiconductor wafer having a patterned photoresist layer. The apparatus also includes an electrically conductive coil disposed above the top of the chamber internal region. An H2O vapor supply line is configured to supply H2O vapor to the chamber internal region. The apparatus includes a first power supply configured to supply radio frequency power to the coil. The radio frequency power supplied to the coil is used to induce an electric current in the chamber internal region. The induced electric current transforms the H2O vapor into H ions, H radicals, O ions, and O radicals. The apparatus further includes a second power supply configured to supply radio frequency power to the semiconductor wafer support structure. The radio frequency power supplied to the semiconductor wafer support structure causes the semiconductor wafer support structure to have a bias voltage. The bias voltage attracts the H ions and the O ions to the patterned photoresist layer of the semiconductor wafer. Upon reaching the patterned photoresist layer of the semiconductor wafer, the H ions and the O ions react to remove at least a portion of the patterned photoresist layer.
The advantages of the present invention are numerous. Most notably, the apparatus and method for using H2O vapor as a processing gas as disclosed in the present invention avoids the problems of the prior art by effectively stripping the photoresist material having the photoresist crust without causing the photoresist crust to pop or be undercut. Thus, the present invention eliminates the problems of the prior art by using H2O vapor as a safe, effective, and economical processing gas for stripping photoresist material having a photoresist crust.
Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention.